Donald Trump soared into a poll lead in the race for the White House as Hillary Clinton's plans for a "Convention of hope" descended into infighting and angry protests, with some Democrats saying they would prefer to vote for her Republican rival.

Donald Trump soared into a poll lead in the race for the White House as Hillary Clinton's plans for a "Convention of hope" descended into infighting and angry protests, with some Democrats saying they would prefer to vote for her Republican rival.

Ms Clinton is due to become the first female presidential nominee of a major US political party at the Democratic Convention, which began in Philadelphia last night.

It was billed as a week of optimism, laying out a vision of unity and progress, contrasting with Mr Trump's dark and foreboding descriptions of a country in crisis.

Former president Bill Clinton is due to laud the abilities of his wife in a speech tonight followed by a glowing endorsement from President Barack Obama tomorrow setting out how she would secure his legacy.

But Ms Clinton's message, captured in the slogan "Stronger Together", was overshadowed by ugly scenes as thousands of angry party members loyal to Bernie Sanders, her left-wing rival for the nomination, took to the streets in 40C heat.

The protests were much larger than those against Mr Trump - considered one of the most divisive politicians in modern American history - at the Republican convention in Cleveland last week.

It followed a scandal in which leaked internal Democratic Party emails showed officials had plotted against Mr Sanders in favour of Ms Clinton.

The furore centres around allegations, raised more than six months ago, that Debbie Wasserman Schultz and her staff at the DNC were biased in favour of Ms Clinton.

They said that the schedules of debates, fund-raising and access to a supporter database were proof that the DNC was tying to help the establishment candidate defeat the insurgent Vermont senator.

And last night the Democratic National Committee offered its "deep and sincere apology" to Mr Sanders, his supporters and the entire party for what it calls "the inexcusable remarks made over email".

Atheist

The statement from incoming interim party leader, Donna Brazile, and six other officials said the comments in the emails "do not reflect the values of the DNC or our steadfast commitment to neutrality during the nominating process".

On Friday, supporters of Mr Sanders received what they said was proof of their suspicions, when leaked emails revealed that members of the DNC had been plotting against Mr Sanders.

One exchange showed that they planned to try to expose him as an atheist. An email from May 2016 sent from DNC chief financial officer Brad Marshall suggested that they should "get someone to ask" Mr Sanders about his views on religion.

"It might make no difference, but for KY and WVA can we get someone to ask his belief. Does he believe in a God. He had skated on saying he has a Jewish heritage. I think I read he is an atheist," wrote Mr Marshall.

"This could make several points difference with my peeps. My Southern Baptist peeps would draw a big difference between a Jew and an atheist," he added.

Ms Wasserman Schultz, who announced on Sunday night that she is to stand down as head of head of the Democratic National Committee (DNC), was repeatedly booed and mocked by supporters of Mr Sanders as she tried to speak yesterday morning.

A 1,200-strong group of pro-Sanders delegates may also challenge the nomination of Tim Kaine, the Virginia senator, as her running mate, over his policies on trade and Wall Street regulations. A challenge to his nomination could lead to party infighting playing out on the convention floor.

The pavement on Broad Street in Philadelphia was flooded yesterday with supporters of Mr Sanders as they marched to the convention hall. Among them was Corinne Dodge, a retired school teacher from New Hampshire who said Mr Sanders had "absolutely" been robbed of the nomination by the Democratic National Committee, and she was holding out hope of a convention coup to nominate him. Protesters chanted "Hell no, we won't vote for Hillary", wore "Hillary for Prison" T-shirts, and carried "You lost me at Hillary" signs. They also shouted "Lock Her Up", the same rallying cry used by Republicans about Ms Clinton.

Shana Lin, a Democrat and Sanders supporter from Virginia, said: "The system is rigged. At this point I think Trump is a marginal step up."

Mr Sanders addressed his delegates yesterday ahead of the opening of the convention, with cheers turning to boos when he said: "We have got to defeat Donald Trump and we have got to elect Hillary Clinton and Tim Kaine."

A national CNN poll showed Mr Trump on 44pc, Ms Clinton at 39pc, and the Libertarian candidate Gary Johnson on 9pc. A gleeful Mr Trump said: "The Democrats are in a total meltdown."

Meanwhile, the FBI said it is investigating how the thousands of Democratic National Committee emails were hacked, a breach that Hillary Clinton's campaign maintains was committed by Russia to benefit Donald Trump.

A statement from the FBI confirmed that it is "investigating a cyber intrusion involving the DNC", adding that "a compromise of this nature is something we take very seriously."

WikiLeaks posted emails Friday that suggested the DNC was favouring Ms Clinton over her rival Mr Sanders during the primary season. Clinton's campaign pointed to a massive hacking of DNC computers in June that cybersecurity firms linked to the Russian government.

Trump dismissed as a "joke" claims by Ms Clinton's campaign that Russia is trying to help him by leaking thousands of emails from the Democratic National Committee.

"The new joke in town is that Russia leaked the disastrous DNC emails, which should have never been written (stupid), because Putin likes me," Trump wrote as part of a series of Tweets.

"Hillary was involved in the email scandal because she is the only one with judgement (sic) so bad that such a thing could have happened."

The hacking enraged die-hard Sanders supporters who have long claimed that the DNC had its finger on the scale throughout the primaries.

The disclosures prompted the resignation of DNC Chairwoman Debbie Wasserman Schultz on the eve of the party's convention in Philadelphia, where Clinton is expected to officially accept the nomination for president.

It wasn't immediately clear how WikiLeaks received copies of the internal Democratic emails.

Democratic Party officials learned in late April that their systems had been attacked after they discovered malicious software on their computers.

A cybersecurity firm they employed found traces of at least two sophisticated hacking groups on the Democrats' network - both of which have ties to the Russian government.

Those hackers took at least one year's worth of detailed chats, emails and research on Donald Trump, according to a person knowledgeable about the breach who wasn't authorised to speak publicly about the matter.

Director of National Intelligence James Clapper has said US officials have seen indications of foreign hackers spying on the presidential candidates, and that they expect more cyber threats against the campaigns.

Russian presidential spokesman Dmitry Peskov would not comment on allegations that Russia is behind the leaked emails, instead pointing to statements by Trump's son, Donald Trump Jr, dismissing the claims.

"To lead their convention with that tells me they really are trying to move away from what the issues are going to be in this campaign. It's pretty absurd."

Trump told 'The New York Times' last week that he would decide whether to protect America's Nato allies against Russian aggression based on whether those countries "have fulfilled their obligations to us," hinting that he might ­pivot away from the decades-old agreement.

Some Republicans opposed to Trump have indeed sought to cast him as pro-Putin, a position that would put him at odds with both Republican and Democratic foreign policy.